An elastic tissue in the biology body is composed by different compositions. A vessel wall, for example, is mainly composed by collagen fibers, elastins and smooth muscle cells, elastic modulus of these compositions are quite different from each other. If an accurate distribution map showing elastic modulus of a two-dimensional vessel wall can be obtained, compositions of the vessel wall can be distinguished, and the composition distributions of the vessel wall can be obtained. For an atherosclerotic plaque, the composition distributions of lipids, blood clots, fiber tissues, calcified tissues and so on can be obtained.